The present invention relates to a polycrystal silicon rod. More specifically, it relates to a polycrystal silicon rod formed of a high-purity polycrystal silicon of a semiconductor grade having a reduced number of surface pores.
The most common process for producing a high-purity polycrystal silicon comprises the steps of heating a filament of a high-purity silicon with an electric current to cause a reaction of trichlorosilane on the filament, thereby depositing a rod-shaped polycrystal silicon.
In the deposition of polycrystal silicon, a factor having the greatest influence on its productivity is deposition speed. It has been known that the higher the deposition temperature is, the higher the deposition speed of polycrystal silicon is. However, it has also been known that when the deposition temperature is increased, the morphology of the surface of a deposited rod is degraded and the silicon rod surface has objects very similar in shape and size to a popcorn. Polycrystal silicon having a bad morphology (to be simply referred to as "popcorn" hereinafter) easily takes in impurities, an etching solution tends to remain after etching, and pores exist inside the polycrystal silicon, and in consequence, an adverse effect is exerted on monocrystals in particular at the time of pulling up the monocrystals and monocrystals not desirable as a product are produced. Because of the above reasons, the deposition temperature cannot be increased much. JP-A 55-16000 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") describes that the throughput and the morphology of polycrystal silicon conflict with each other.